Cellular morphogenesis is an essential part of animal development and growth. During this process, cells coordinately change shape, migrate, and may fuse. These processes are executed by molecules called effectors. Such effectors have been identified in several model systems and include the cytoskeleton and determinants of cell polarity. The sex-, tissue-, position-, and time-specificity of morphogenesis is determined by regulators, such as transcription factors. How transcriptional regulators are linked to the effectors in a gene network (GN) for morphogenesis is not well understood in nearly any system, but such knowledge is required to predict how perturbations could lead to morphogenetic changes during development, cancer, and the evolution of form. Elucidating this GN would also impact our understanding of wound healing and regeneration. Our long-term goal is to completely delineate the GN architecture governing the morphogenesis of a novel, simple and sexually dimorphic model structure, the tail tip of Caenorhabditis elegans. The tail tip is composed of four cells which-in males only-radically alter their shape and position at the end of larval development. Previous studies identified a master regulator for tail tip morphogenesis (TTM), the transcription factor DMD-3 (homologous to DMRT1 in humans, which specifies male fates). Without DMD-3, TTM completely fails. Also, DMD-3 is sufficient to cause TTM when ectopically expressed in hermaphrodites. Here, we will test how DMD-3 is linked to the effectors of TTM. Specific Aim 1 will test this hypothesis by a series of pairwise molecular epistasis experiments with DMD-3 and a set of key effectors of TTM which the Fitch lab previously identified in a postembryonic-RNAi screen. In these experiments, a gene X (e.g. DMD-3) will be knocked down and the effect on the transcription, translation or subcellular localization of a gene product Y will be analyzed. Network analysis will be used to identify auto-regulatory, feedback, feed-forward, or other system controls important for the GN. Specific Aim 2 addresses the question of which other genes are downstream of DMD-3 and what contributes to the sufficiency of DMD-3 for TTM. Tail-tip-specific transcriptome analyses will be performed on samples from wild-type males and hermaphrodites, males deficient for DMD-3, and hermaphrodites misexpressing DMD-3. The expected outcome is a framework for the GN architecture downstream of DMD-3 and an understanding of how it governs the localization or expression of key effectors of cell shape change. This GN will lay the requisite foundation for future studies on the molecular mechanisms underlying these interactions and how they affect cell-biological modules. These results are expected to have a positive impact on medicine, as they could identify key conserved genes that control morphogenesis, thus providing new targets for drugs to mitigate the effects of morphogenetic defects or cancer, or to aid wound healing.